It appears that guest accounts seem to be just adding to the player base while I've been testing.
It depends on you. The retrieved device ID is consistent from the same Device. If you use this device ID directly to login, players will always access the same account. Meanwhile, you can append randomly generated string to the device ID so that there can be multiple accounts on the same device.
LoginWithAndroidDeviceID and LoginWithIOSDeviceID, or even LoginWithNintendoSwitchDeviceId is only one of many login methods, you may refer to Login basics and best practices, to implement or improve the login flow of your game.
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